public class TestConstant {
    public static void main(String args[]){
        final double PI = 3.14;   //final 定义常量    ,常量的命名：全用大写字母，单词之间下划线隔开
        int r = 4;
        double area = PI*r*r;
        double circle = 2*PI*r;

        System.out.println("area: "+area);
        System.out.println("circle: "+circle);

    }
}